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Mac 250 Bugging me still!


Nicktaylor

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One of my second hand Macs has never worked properly. I have tried changing the sensor,wireset etc etc. Today I thought I would take some measurements. 5v arriving to power the hall effect . Impedance measure is 30k with the N pole of magnet off and 15M with it on. This suggests the wiring is working as is the sensor. What component on the board might now need checking?. This unit will soon be spares or repair, or a part exchange!
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This sounds like the gobo or color wheel has been taken off the motor and not properly realigned when it was put back on. Old Mac 250s only check the status of the hall switch between each motor step, not continuously as the wheel is moving. If the wheel isn't lined up correctly the magnet can move past the sensor without being detected.

 

What you need to is loosen whichever wheel is causing you problems and then power up the unit, making sure you don't strike the lamp! Take the top cover off the head and put your multimeter on the hall sensor. Turn the wheel until the magnet triggers the switch. Now just tighten up the grub screws that holds the wheel ( you'll need about 3 pairs of hands for this :) ). Close up the head and reset the unit and it should all be sorted.

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Its amazing but the colour wheeel has welded itself onto the stepper motor shaft. I have that module out, both grubscrews right out and still cant shift the wheel! I suspect I will need to get a replacement module and part ex this one to someone who can sort it!
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Its not welded. What usually happens is that the grub screws slightly deform the motor shaft, and because the colour wheels hub is a very close fit anyway its tends to get stuck. You could try putting a flat-head screw driver between the colour wheel and the metal plate and twisting it. This should push the wheel off the motor. Failing that, cut the motor shaft with a hacksaw and just get a new motor.
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Indeed, pre smoking ban nightclub gunk combined with heat could make colour wheels incredibly difficult to get off, I had this on a load of MAC500s I serviced years ago. Some of them quite literally took 2 large flathead screwdrivers being twisted and plenty of brute force, some bending of the colour wheels, plenty of aggro etc. Sometimes the screwdriver blades needed propping up slightly on another screwdriver or similar to get the required leverage angle.

 

Oh, and Roboscan 518 shutters are even worse!

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